Dust seal high performance breaker

ABSTRACT

Disclosed is a high performance dust or explosion proof electrical circuit breaker. In one embodiment the breaker is provided with a dust seal flap for venting arcing gases to atmosphere while at the same time substantially reducing the entry of dust and dirt into the breaker housing. In a second embodiment the dust seal is replaced by a fine mesh screen for increased safety when the breaker is used in an atmosphere which may present a danger of explosion.

[11] 3,780,249 1451 Dec. 18, 1973 United States Patent [1 1 Harper 200/l 44 R 200/168 G 3,582,966 6/1971 Strobel....... 2,158,317 5/1939 DUSTSEAL HIGH PERFORMANCE BREAKER [75] Inventor:

George S. Harper, Cambridge, Md.

Primary Examiner-Robert K. Schaefer [73] Ass1gnee: Airpax ElectronicsIncorporated, Assistant Examiner--William J. Smith AttorneyRobert E.LeBlanc et al.

4 Cambridge, Md.

[22] Filed: Apr. 28, 1972 ABSTRACT Disclosed is a high performance dustor explosion proof electrical circuit breaker. In one emb 21 Appl. No.:248,406

..2 1 00 44 odimem {2%} 3.2 i. 5101 19/05 me eeeekee e eeeeeee wee lzoo/144 R, 168 0,

ing arcing gases to atmosphere while at the same time 58 F1 Id fSea l eo R ZOO/I46 R substantially reducing the entry of dust and dirt into thebreaker housing. In a second embodiment the dust seal is replaced by afine mesh screen for increased safety when the breaker is used in anatmosphere which may present a danger of explosion.

S T N m .IP S mm A RT .mS D E W N U m 1 3,663,779 5/1972 Gerlach ZOO/168G 2,650,964 9/1953 200/168 G 17 Claims, 8 Drawing Figures RazdowPATENTEI] m 18 1973 SIEEI 1 BF 2 FIG. 2

FIG.I

DUST SEAL HIGH PERFORMANCE BREAKER This invention relates to a highperformance electrical circuit breaker for use under adverse conditions.In particular, it is directed to an electromagnetic circuit breakerwhich may be used in dusty atmosphere or under conditions in which theatmosphere may present a danger of explosion.

As is well known, the opening and closing of the electrical contacts ofa circuit breaker are often accompanied by the creation of .anelectricalarc across the contacts. This electrical arcing causes increases in heatand pressure within the circuit breaker housing. The arcing across theelectrical contacts may be particularly severe when the contacts areopened in response to an overcurrent flowing through the breaker. Inorder to minimize arcing and theaccompanying heat and pressure withinthe breaker it is customary to provide a so called arc chute in the arcchamber of the breaker adjacent the area in which the arc is formed.While these are chutes may have some value, they do not completelyeliminate breaker arcing.

Because of the increased pressures of the arc gases created in the areaof the circuit breaker contacts many circuit breakers are provided withvents for venting the arc gases generated in the arc chamber of thecircuit breaker to atmosphere. This not only releases the excessivepressures generated in the arc chambers but also helps to more rapidlydissipate heat from the breaker which might otherwise have an adverseaffect on the circuit breaker components. However, vented circuitbreakers are notsuitable for use in many situations where contaminantsin the atmosphere may gain access through the vents in the circuitbreaker housing to the working components of the breaker. For example,it has been found that when a circuit breaker is incorporated in thecompartment of a deisel engine locomotive, dust and dirt from the engineatmosphere tends to fill and clog the circuit breaker vents so as toprevent proper exhaust of the arc gases from the circuit breakerhousing. In addition, the dust and dirt collects on the electricalcontacts and other moving parts of the circuit breaker mechanism furtheradversely affecting circuit breaker operation to the point where thetripping characteristics of the breaker are no longer reliable.

There are other situations in which vented circuit breakers areundesirable. For example, vented circuit breakers are not acceptable foruse in the bilge area of a marine vessel or boat. As is well known, thebilge area of a boat tends to trap gasoline vapors from the boat engineand when these vapors build up to a sufficient degree, they present adanger of explosion. Needless to say, a marine explosion can be fatal.The buildup of gasoline vapors in the bilge presents a serious safetyproblem to the operator of a boat or other marine vessel. These gasolinevapors may be ignited when the excessive pressures in the circuitbreaker accompanying the electrical arc across the circuit breakercontacts causes a small flame to be actually blown out of the circuitbreaker through the exhaust vents into the potentially explosivegasoline vapor atmosphere.

In order to cope with these problems and dangers encountered whencircuit breakers are operated under such adverse conditions, it has beenproposed to use under circumstances of this type electrical circuitbreakers which are contained in completely sealed or completely closedhousings so that no gases may be vented to atmosphere and nocontaminants from the atmosphere may gain access to the interior of thecircuit breaker. While completely sealed circuit breakers find someutility in adverse atmospheres, the fact that they are completely closedpermits the buildup in the circuit breaker of excessive amounts of heatand pressure due to contact arcing. As a result, completely enclosedcircuit breakers of this type generally possess very poor electricalshort circuit features and they are not considered to be highperformance breakers.

The present invention overcomes these and other problems by providingahigh performance circuit breaker which can be used under adverseconditions and in particular provides a breaker which can be used in adusty or a dirty atmosphere such as an engine compartment of a deisellocomotive or in a potentially explosive atmosphere such as the bilge ofa marine vessel. In one embodiment of the present invention, the circuitbreaker is provided with a novel silicone rubber seal around the circuitbreaker handle. Further, the circuit breaker housing or case is providedwith an aperture communicating with the interior of the arc chamber ofthe breaker. In order to minimize the entry of dust, dirt and othercontaminants fromthe atmosphere, this aperture is closed off by amovable dust seal, preferably in the form of a flexible flap restrainedat one end but having its other end free tomove under the influence ofincreased are created pressures in the interior of the breaker. Whencontact arcing occurs, the elevated pressure in the arc chamber causesthe flap to move and open the aperture exhausting the arc gases toatmosphere and relieving the excessive amounts of heat and pressure inthe circuit breaker. During those times when no arcing occurs across thecircuit breaker contacts, the resilient nature of the flexible dust sealflap causes it to return to its initial position closing the exhaustaperture and sealing the circuit breaker against the entry of dust anddirt.

In a second embodiment of the present invention the dust flap seal isreplaced by a fine wire mesh screen. This screen acts as a flamearrestor for the arc chamber and while it permits the arc gases and theexcessive heat and pressure accompanying them to vent through theexhaust aperture to the atmosphere the screen prevents any flame frombeing blown out of the arc chamber and substantially increases thesafety with which the circuit breaker may be used in a potentiallyexplosive atmosphere such as the bilge area of a marine vessel. It hasbeen found that in order to adequately operate as a flame arrestor, asingle layer screen constructed in accordance with this invention shouldbe provided with relatively small openings. In particular,

.it has been found that the screen should have openings no larger than30 mesh and a single layer of 60 mesh screen is preferred. If multiplelayers of screen are used, a larger mesh size (lower mesh number) may beemployed but in any event, the combined effect of the multiple layersshould be to provide an effective mesh opening no larger than 30 mesh.

It is therefore, one object of the present invention to provide anapproved high performance circuit breaker.

Another object of the present invention is to provide a high performancecircuit breaker usable under adverse conditions.

Another object of the present invention is to provide a high performanceelectrical circuit breaker usable in a dusty and dirty atmospheresuch asthe atmosphere surrounding the engine of a diesel locomotive.

Another object of the present invention is to provide a high performancecircuit breaker usable in a potentially explosive atmosphere such as thebilge of a marine vessel.

Another object of the present invention is to provide an improved highperformance dust seal circuit breaker.

Another object of the present invention is to provide a high performancecircuit breaker incorporating a dust seal in the form of a flexible andresilient flap for venting the arc chamber of a circuit breaker housingto atmosphere.

Another object of the present invention is to provide a high performancecircuit breaker incorporating a flame arrestor vent for the circuitbreaker arm chamber.

Another object of the present invention is to provide a flame arrestingvent for a circuit breaker arc chamber in the form of a fine wire meshscreen having oepnings no later than approximately 30 mesh.

Another object of the present invention is to provide a high performancecircuit breaker with an improved silicone rubber seal for the circuitbreaker operator or handle. 7

These and further objects and advantages of the invention will be moreapparent upon reference to the following specification, claims andappended drawings wherein:

FIG. 1 is a front view of a magnetic circuit breaker constructed inaccordance with this invention.

FIG. 2 is a side view of the circuit breaker of FIG. 1 with portionsbroken away and parts in section to more clearly showthe novel featuresof the present invention.

FIG. 3 is a top plan view of the circuit breaker of FIG. 2 again withparts broken away and parts in section for the sake of clarity.

FIG. 4 is a plan view of the dust seal flap forming a part of thecircuit breaker of FIGS. l-3.

FIG. 5 is a side view similar to FIG. 2 but with the seals omitted toshow the supporting structure.

FIG. 6 is a top plan view similar to FIG. 3 again with the seals omittedto more clearly show the supporting structure for the seals.

FIG. 7 is a partial side view similar to FIG. 2 showing a modifiedembodiment in which the dust seal of flap is replaced by a fixed flamearresting fine mesh wire screen.

FIG. 8 is a top plan view of the flame arresting metal screen of thecircuit breaker of FIG. 7.

Referring to the drawings, the novel high performance circuit breaker ofthe present invention is generally indicated at 10 in FIG. 1 asincluding a housing 12 formed of mating sections or housing halves l4and 16. Housing 12 is preferably molded from a black colored phenolicmaterial and after the operating mechanism of the breaker is insertedthe two halves, 14 and 16 are joined together in a conventional mannerby screws or the like to form a single unitary housing 12. The partingline defining the two housing halves I4 and 16 is indicated at 18. Theoperating mechanism of the circuit breaker forms per se no part of thepresent invention and has been omitted for the sake of clarity. It isunderstood that the circuit breaker mechanism is preferably of themagnetic type but it is understood that the features of the presentinvention are equally applicable to other types of circuit breakermechanisms including the bi-metallic or thermal breakers. By way ofexample only, the operating mechanism of the breaker of the presentinvention may be of the type disclosed in the assignees U.S. Pat. No.3,412,351 or in assignees U.S. Pat. No. 3,486,140.

Referring to FIGS. 2 and 3, housing 12 is provided at its front or facewith an outwardly extending rectangular boss 20 through which projectsthe operator or handle 22 manually movable between the of positionillustrated in the drawings and the on position as indicated by thedouble ended arrow 24 in FIG. 2. Handle 22 is preferably made fromasuitable electrically insulating plastic such as nylon and is formedintegral with a semi-cylindrical handle disc 26. Passing through thecenter of semi-cylindrical disc 26 is a pivot pin 28 which has its outerends supported by the walls of housing 12. In this way, the nylon discwhich forms a bearing material is free to rotate about pin 28, betweenthe in and off positions of the handle. Formed integral with handle disc26 are a pair of outwardly extending ears one of which is illustrated at30 FIG. 2 which are apertured as at 32 to receive a pin for connectingthe handle disc to a collapsible toggle linkage mechanism of the typeshown and described in the two above-identified patents. When the handleis in the off position, as illustrated, the circuit breaker contacts(not shown) are closed and when the handle is moved upwardly in FIG. 2to the on position, the contacts are closed in a well known manner.Tripping of the toggle by an overcurrent causes the contacts to open andthe handle to move to the off position. 7

Referring to FIGS. 5 and 6 in conjunction with FIGS. 1 to 3 boss 20 isprovided with an aperture 34 through which that handle 22 passes andthis aperture which is of rectangular configuration communicates with asecond larger rectangular aperture 36 in the circuit breaker whichlarger aperture defines a groove, 38 extending completely around thehandle. Positioned with its outer edges received in the groove 36 is ahandle seal 40 formed as a sandwich construction and comprising a rigidouter support 42, a rigid inner support 44 and an intermediate flexiblesealing member 46 preferably formed of silicone rubber. By way ofexample only, outer support 42 may be formed of a suitable black coloredphenolic having printed on it in white letters the word off above handle22 as illustrated at 48 in FIG. 1 and theword on? beneath the handle.The word on is obscured when the handle is in the downward positionillustrated in the drawings and the word off is obscured when the handleis in its uppermost position. Each of the supports 42 and 44 as well asthe silicone rubber seal are formed from thin rectangular sheets andeach is provided with a central rectangular aperture through which thehandle passes. However, the central aperture in sealing member 46 issmaller than the apertures in the supports 42 and 44 so that sealingmember 46 is the only one which actually touches handle disc 26.Preferably silicone rubber seal 46 engages the handle or disc all theway around to tightly seal the handle aperture against the entry ofdust, dirt and the like. The silicone rubber forms a good sliding sealwith the disc portion of handle 22 and permits the handle to be moved upand down because of the resilient and flexible nature of the siliconerubber while at all times maintaining a good dust seal.

An additional important feature of the circuit breaker illustrated inFIGS. l-3 is the incorporation in the housing 12 of a dust seal flap 50adapted to close off an exhaust aperture 56 through the housingcommunicating with the circuit breaker arc chamber 58. Flap 50 is formedfrom a thin flat sheet of suitable plastic material preferable mylar? asillustrated in FIG. 4 and is bent at one end around an imaginary lineindicated at 52 in FIG. 4 to form the turned over end 54 illustrated inFIG. 2.

Flap 50 closes off aperture 56 which is best seen in FIGS. 5 and 6. Thisaperture includes at its lower end a rectangular cross section portion58 forming a part of the circuit breaker arc chamber and an enlargedupper portion 60. Enlarged upper end 60 defies a groove 62 in which isplaced the turned .over end 54 of the mylar flap 50. Enlarged portion 60of the opening also defines a pair of shoulders 64 and 66 whichshoulders slope outwardly or upwardly in FIG. 5 and terminate in anajoining ledge 68. The two edges 70 and 72 of flap 50 illustrated inFIG. 4 normally rest against the inclined respective shoulders 64 and 66an'd the remote end 74 of the flap rests against the shoulders and ledgeto tightly seal passageway 56 against the entry of dust, dirt and thelike by the resilient nature of the turned over end 54 bearing againstthe sides of groove 62 as illustrated in FIG. 2. However, when anoverpressure occurs 'in the arc chamber 58, the base of the V formed byturned over end 54 acts as a pivot and the free end 74 of the flap movesoutwardly away from the housing and ledge 68 in the direction of thearrow 76 in FIG. 2 to permit the excess pressure and some of the heat toexhaust to atmosphere from the arc chamber. When the overpressure hasbeen relieved, the resilient nature of the mylar strip causes the flapto return to the position illustrated in FIG. 2 to again seal theopening 56 against the entry of dust, dirt and other contaminantswhich-may be in the atmosphere surrounding the circuit breaker.

FIG. 7 shows a modified construction in which housing 12 is counterboredas at 80 to receive a fine. wire mesh screen 82 which closes off apassageway 84 communicating with the circuit breaker arc chamber. FIG. 8is a top plan view of the wire mesh screen 82 which is preferably ofconventional woven wire mesh construction and in the preferredembodiment has mesh openings of 60 mesh. It is understood that theremainder of the circuit breaker embodiment illustrated in FIGS. 7 and 8is identical in constructin to the embodiment previously described withrespect to FIGS. 1-6. It has been found that the fine wire mesh screen82 acts as a flame arrestor so that the modified circuit breaker of FIG.7 is suitable for usein potentially explosive atmospheres such as marinebilges where gasoline vapors tend to collect and otherwise might beexploded by a flame blowing out through vents in the circuit breakerhousing from the arc chamber. Screen 82 may be secured in thecounterbore 80 in any suitable manner such as by the application of asuitable adhesive to the outer edges of the screen. In. order to besuitable for use in a potentially explosiveatmo'sphere, it has beenfound that the openings in the single layer wire mesh 82 can be nolarger than approximately 30 mesh and as previously indicated, thepreferred size for the mesh openings is 60 mesh. If multiple layers ofscreen material are used for the screen 82, then larger mesh sizes(lower mesh numbers) can be used but in any event the effective openingsformed by the multiple layers should be the equivalent of 30 meshsize'or smaller.

It is apparent from the above that the present invention provides animproved high performance circuit breaker for use under adverseconditions and particularly a circuit breaker in one embodiment suitablefor in a dusty atmosphere and in another embodiment, a circuit breakersuitable for use in a potentially explosive atmosphere. In both oftheembodiments, the handle aperture is closed off by a novel siliconerubber seal which remains in sealing engagement with the handle duringall handle movements. In the dust seal embodiment the breaker housing.isin addition to the handle seal provided with a resilient and flexiblevent flap seal so that excessive pressures associated with contactarcing may be vented to atmosphere whereas during the vast majority ofthe time the flap is closed and the circuit breaker tightly sealedagainst the entry of dust.

Changes and modifications where desired are readily apparent. Forexample, plastic mesh constructions may be substituted for the wovenwire meshes, materials other than mylar may be used for the dust sealflap and other appropriate materials may be substituted for the elementsof the handle seal 40 although silicone rubber has been foundparticularly suited for engagement with the handle disc 26. In someinstances, the back support 44 of FIG. 2 may be completely eliminatedand the silicone rubber seal 46 held in place between a portion of thecircuit breaker housing and the support 42.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope-of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which-come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In a circuit breaker having a housing and a handle extendingoutwardly from the housing, the improvement comprising sealing meansengaging said handle to. establish a seal between said handle andhousing, an arc' chamber gas vent in said housing, and a dust sealacross said vent for closing off said vent against the entry of dustinto said housing while permitting gases to exhaust to atmosphere fromsaid housing through said vent.

2. Apparatus according to claim 1 wherein said dust seal comprises amovable flap.

3. Apparatus according to claim 1 wherein said sealing means comprisesat least one rigid support member having a central aperture throughwhich said handle passes, and a sealing member supported in said housingby said support member,'said sealing member having a central aperturewith its edges in sealing contact with said handle.

4. Apparatus according to claim 3 wherein said support member andsealing member apertures are rectangular.

5. Apparatus according to claim 3 wherein said housing is provided witha groove, the outer edges of said support and sealing members beingreceived in said groove.

6. Apparatus according to claim 3 wherein said sealing member is madefrom a flat strip of silicone rubber.

7. Apparatus according to claim 6 wherein said support member is madefrom a flat strip of phenolic mate-- rial.

8. Apparatus according to claim 7 including a second support strip ofplastic material on the side of said sealing member remote from saidphenolic strip.

9. A dust seal high performance circuit breaker comprising a housing,said housing having a first aperture, a handle extending through saidfirst aperture, first sealing means in said aperture establishing afirst seal between said housing and said handle, said housing have asecond aperture, and dust seal means on said housing for sealing saidsecond aperture against the entry of dust into said housing whilepermitting gases to exhaust from said housing through said secondaperture.

10. A circuit breaker according to claim 9 wherein said dust seal meanscomprises means normally closing off said second aperture but movable inresponse to an overpressure in said housing to open said secondaperture.

11. A circuit breaker according to claim 10 wherein said dust seal meanscomprises a flap resiliently biased closed but pivoted to open upon arise in pressure within said breaker housing;

12. A high performance circuit breaker for use in potentially explosiveatmospheres comprising a housing, said housing having a first aperture,a handle extending through said first aperture, sealing means in saidfirst aperture establishing a seal between said housing and said handle,said housing having a second aperture, and flame arresting means on saidhousing for preventing contact arc flames from being blown out of saidhousing through said second aperture.

13. A circuit breaker according to claim 12 wherein said flame arrestingmeans comprise a fine mesh screen extending across said second aperture.

14. A circuit breaker according to claim 13 wherein said screen has aneffective-mesh size no larger than 30 mesh.

15. A circuit breaker according to claim 13 wherein said screencomprises a single layer wire mesh having a mesh size of about 60 mesh.

16. A dust seal high performance circuit breaker comprising a housing,said housing having a first aperture, a handle extending through saidfirst aperture, first sealing means in said aperture establishing aflrstseal between said housing and said handle, said housing having a secondaperture,'and dust seal means on said housing for sealing said apertureagainst the entry of dust into said housing while permitting gases toexhaust from said housing through" said second aperture, said dust sealmeans comprising means normally closing off said second aperture butmovable in response to an overpressure in said housing to open saidsecond aperture, said dust seal means comprising a flap resiliently biasclosed but pivoted to open upon a rise in pressure within said breakerhousing, said flap comprising a strip of plastic turned over at one end,said circuit breaker housing including a groove. adjacent said secondaperture receiving said turned over end of said flap.

17. A circuit breaker according to claim 16 wherein said flap is made ofresilient plastic.

zgz g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,780,249December 18, 1973 Patent No. Dated Inventor(s) George S. Harper It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 15, "am" should read arc- Column 4, line 19, "in" shouldread ---on- Signed arid sealed this 9th dayof April 19m;

(SEAL) Attest:

EDWARD I=I..FLETCPMH,JH. C MARSHALL DAN'N Attesting Officer Commissionerof Patents g g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION3,780,249 December 18, 1973 Patent No. Dated Inventor(s) George S.Harper It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 3 line 15, "arm" should read --ar c- Column 4, line 19, "in"should read -on- Y Signed arid sealed this 9th day of April 1971;.

(SEAL) Attest;

EDWARD mmrmctmamra c MARSHALL DANN Attesting Officer Commissioner ofPatents

1. In a circuit breaker having a housing and a handle extending outwardly from the housing, the improvement comprising sealing means engaging said handle to establish a seal between said handle and housing, an arc chamber gas vent in said housing, and a dust seal across said vent for closing off said vent against the entry of dust into said housing while permitting gases to exhaust to atmosphere from said housing through said vent.
 2. Apparatus according to claim 1 wherein said dust seal comprises a movable flap.
 3. Apparatus according to claim 1 wherein said sealing means comprises at least one rigid support member having a central aperture through which said handle passes, and a sealing member supported in said housing by said support member, said sealing member having a central aperture with its edges in sealing contact with said handle.
 4. Apparatus according to claim 3 wherein said support member and sealing member apertures are rectangular.
 5. Apparatus according to claim 3 wherein said housing is provided with a groove, the outer edges of said support and sealing members being received in said groove.
 6. Apparatus according to claim 3 wherein said sealing member is made from a flat strip of silicone rubber.
 7. Apparatus according to claim 6 wherein said support member is made from a flat strip of phenolic material.
 8. Apparatus according to claim 7 including a second support strip of plastic material on the side of said sealing member remote from said phenolic strip.
 9. A dust seal high performance circuit breaker comprising a housing, said housing having a first aperture, a handle extending through said first aperture, first sealing means in said aperture establishing a first seal between said housing and said handle, said housing have a second aperture, and dust seal means on said housing for sealing said second aperture against the entry of dust into said housing while permitting gases to exhaust from said housing through said second aperture.
 10. A circuit breaker according to claim 9 wherein said dust seal means comprises means normally closing off said second aperture but movable in response to an overpressure in said housing to open said second aperture.
 11. A circuit breaker according to claim 10 wherein said dust seal means comprises a flap resiliently biased closed but pivoted to open upon a rise in pressure within said breaker housing.
 12. A high performance circuit breaker for use in potentially explosive atmospheres comprising a housing, said housing having a first aperture, a handle extending through said first aperture, sealing means in said first aperture establishing a seal between said housing and said handle, said housing having a second aperture, and flame arresting means on said housing for preventing contact arc flames from being blown out of said housing through said second aperture.
 13. A circuit breaker according to claim 12 wherein said flame arresting means comprise a fine mesh screen extending across said second aperture.
 14. A circuit breaker according to claim 13 wherein said screen has an effective mesh size no larger than 30 mesh.
 15. A circuit breaker according to claim 13 wherein said screen comprises a single layer wire mesh having a mesh size of about 60 mesh.
 16. A dust seal high performance circuit breaker comprising a housing, said housing having a first aperture, a handle extending through said first aperture, first sealing meaNs in said aperture establishing a first seal between said housing and said handle, said housing having a second aperture, and dust seal means on said housing for sealing said aperture against the entry of dust into said housing while permitting gases to exhaust from said housing through said second aperture, said dust seal means comprising means normally closing off said second aperture but movable in response to an overpressure in said housing to open said second aperture, said dust seal means comprising a flap resiliently bias closed but pivoted to open upon a rise in pressure within said breaker housing, said flap comprising a strip of plastic turned over at one end, said circuit breaker housing including a groove adjacent said second aperture receiving said turned over end of said flap.
 17. A circuit breaker according to claim 16 wherein said flap is made of resilient plastic. 